device/mipi: Move to drivers/mipi

Sounds like we prefer to have this under drivers/ instead of device/.
Also move all MIPI-related headers out from device/ into their own
directory.

Signed-off-by: Julius Werner <jwerner@chromium.org>
Change-Id: Ib3e66954b8f0cf85b28d8d186b09d7846707559d
Reviewed-on: https://review.coreboot.org/c/coreboot/+/57128
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Hung-Te Lin <hungte@chromium.org>
Reviewed-by: Yu-Ping Wu <yupingso@google.com>
Reviewed-by: Nico Huber <nico.h@gmx.de>

src/device/Kconfig

@@ -1,7 +1,5 @@
 ## SPDX-License-Identifier: GPL-2.0-only
 
-source "src/device/mipi/Kconfig"
-
 menu "Devices"
 
 config HAVE_VGA_TEXT_FRAMEBUFFER